A voluntary surrender, as the police define it...

This particular incident wasn't even prompted by a crime. Someone with a clean criminal record happened to buy guns with his tax refund after being put on administrative leave over a work dispute; someone brought this to the attention of the police, who felt it warranted a pre-emptive mental health evaluation. Well, if you can use "warranted" for cases where the police don't bother to get a warrant.

The man has been released, his guns have been returned, and he has not been charged with anything. I hope he sues.

McDonald v Chicago Oral Argument Transcript

The transcript is available here (PDF format). Early takes on the argument indicate that incorporation through the due process clause is almost certain, but incorporation through privileges and immunities clause (Gura's main argument) is unlikely. This is a somewhat disappointing result, since the Slaughterhouse Cases which originally denied the privileges and immunities route are generally accepted to be bad law. But it's not unexpected.